1. Field of the Invention
The present invention generally relates to magnetoresistive devices used in a magnetic head for reading magnetized information from magnetic recording media, and, more particularly, to a spin-valve magnetoresistive device (hereinafter referred to simply as xe2x80x9cSVMR devicexe2x80x9d) utilizing giant magnetoresistive (GMR) effects. A SVMR device is a highly-sensitive magnetoresistive device that detects a magnetoresistive value change in a magnetic layer caused by a minute external magnetic field, and has been attracting more and more attention as a reproduction unit used in a high-density magnetic recording apparatus.
2. Description of the Related Art
FIG. 1 shows the structure of a conventional SVMR device 100. This SVMR device 100 comprises a free magnetic layer 101 formed from a ferromagnetic layer, a non-magnetic conductive layer 102 formed on the free magnetic layer 101, a fixed magnetic layer 103 formed from a ferromagnetic layer on the non-magnetic conductive layer 102, and an anti-ferromagnetic layer 104 formed on the fixed magnetic layer 103. The SVMR device 100 shown in FIG. 1 is a forward-direction laminated type that has a multi-layered structure formed by a thin-film forming technique starting from the bottom layer (which is the free magnetic layer 101 in this case). Also, a SVMR device of a reverse-direction laminated type, which is laminated starting from the anti-ferromagnetic layer 104 as the bottom layer, is known and basically has the same functions as the forward-direction laminated type. In this specification, the SVMR device 100 of the forward-direction laminated type will be described.
In FIG. 1, the magnetic direction of the free magnetic layer 101 is magnetically rotated by a signal magnetic field Hsig from a magnetic recording medium. As the relative angle between the magnetic direction of the free magnetic layer 101 and the magnetic direction of the fixed magnetic layer 103 changes, the magnetic resistance of the SVMR device 100 changes accordingly. When the SVMR device 100 is used as a magnetic head for reproduction, the magnetic direction of the fixed magnetic layer 103 is fixed in the height direction H of the SVMR device 100. When no external magnetic field is applied, the magnetic direction of the free magnetic layer 101 is set in the width direction W of the device 100 and thus is perpendicular to the magnetic direction of the fixed magnetic layer 103. While the magnetic direction of the free magnetic layer 101 is perpendicular to the magnetic direction of the fixed magnetic layer 103, the signal magnetic field Hsig from the magnetic recording medium is in parallel with the magnetic direction of the fixed magnetic layer 103 or with the reverse direction of the magnetic direction of the fixed magnetic layer 103, and is perpendicular to the magnetic direction of the free magnetic layer 101. Accordingly, the magnetic resistance of the SVMR device 100 can be symmetrically detected. Such symmetrical magnetic resistance facilitates the signal processing in the magnetic recording apparatus, and the signal magnetic field Hsig from the magnetic recording medium can be reproduced with high precision.
However, a leakage magnetic field that tilts the magnetic direction of the free magnetic layer 101 exists in the vicinity of the SVMR device 100. Examples of the leakage magnetic field having adverse influence upon the free magnetic layer 101 include a magnetic field generated from the end surface of the fixed magnetic layer 103, an exchange-coupling with the anti-ferromagnetic layer generated between the fixed magnetic layer 103 and the free magnetic layer 101, and a sense current magnetic field formed by a sense current that is applied to detect the magnetic resistance of the SVMR device 100. Under the adverse influence of the leakage magnetic field, the magnetic direction of the free magnetic layer 101 deviates from the direction parallel with the width direction W toward the height direction H. As a result, the magnetic resistance variation of the SVMR device 100 in response to the signal magnetic field Hsig cannot be maintained in the symmetrical state.
To direct the magnetic direction of the free magnetic layer 101 into a parallel direction with the width direction W, a corrective magnetic field for correcting the deviation of the magnetic direction of the free magnetic layer 101 can be applied. In this specification, such a correction magnetic field for canceling a leakage magnetic field is referred to as a bias magnetic field, which is so set that the magnetic direction of the fixed magnetic layer 103 and the free magnetic layer 101 are perpendicular to each to other when no external magnetic field exists in the vicinity of the SVMR device 100.
The size of the SVMR device 100 is determined by the density of a magnetic recorded material to be reproduced. Because of today""s rapid increase in recording density, the distance between a magnetic recording medium and the signal magnetic field Hsig has been shrinking. To read the signal magnetic field Hsig accurately, it is necessary to reduce the width w of the SVMR device 100. However, if the width w of the SVMR device 100 is smaller than the height h of the SVMR device 100, the magnetic direction of the free magnetic layer 101 is liable to tilt into the height direction H due to shape anisotropy. Moreover, the height h needs to be reduced as the width w is reduced, since otherwise it is difficult for the signal magnetic field Hsig to enter in the height direction H.
Meanwhile, the SVMR device 100 that can be actually used in a magnetic head is submicron in size. With a smaller height h of the device 100, the adverse influence of the leakage magnetic field from the fixed magnetic layer 103 is larger. Despite this effect, the height h of the device 100 is becoming smaller as the density of the magnetic recording medium is becoming higher. Accordingly, a magnetostatic leakage magnetic field from the fixed magnetic layer 103 becomes even stronger, and the magnetic direction of the free magnetic layer 101 liable to deviate into a direction parallel to the reverse direction of the magnetic direction of the fixed magnetic layer 103.
Solutions have been suggested to eliminate the problems associated with a small height h of the device 100. One of the solutions suggests a method in which the current direction is adjusted to generate a sense current magnetic field in such a direction that cancels a leakage magnetic field from the fixed magnetic layer 103. However, a sense current of 45 MA/cm2 can generate a magnetic field of only 10 Oe, for instance. In view of this, a great improvement in bias magnetic field cannot be expected from the sense current.
The magnetic quantity of the fixed magnetic layer 103 can be reduced, but the thickness of the fixed magnetic layer 103 is required to be greater than a certain thickness in order to maintain the magnetic characteristics of the SVMR device 100.
Meanwhile, a technique in which a multi-layered structure is used in place of the conventional fixed magnetic layer has been suggested. The multi-layered structure includes a ferromagnetic layer, a reverse parallel coupling intermediate layer, and another ferromagnetic layer, which layers are laminated in that order. This multi-layered structure will be hereinafter referred to as xe2x80x9cmulti-layered fixed magnetic layersxe2x80x9d. In this multi-layered fixed magnetic layer, the magnetic directions of the upper and lower ferromagnetic layers are reverse to each other, with the anti-parallel coupling intermediate layer being interposed. Accordingly, the upper and lower ferromagnetic layers cancel the magnetism of each other, and the leakage magnetic field applied to the free magnetic layer becomes smaller. Since the multi-layered fixed magnetic layer is normally formed by one magnetic material, the upper and lower ferromagnetic layers have the same thickness, which effectively nullifies the effect of the leakage magnetic field on the free magnetic layer.
Taking the function of a SVMR device into account, however, the upper and the lower ferromagnetic layers should be different in thickness so as to improve the magnetic properties such as unidirectional anisotropic magnetic field (Hua) and magnetoresistive effects. More specifically, the ferromagnetic layer in contact with the anti-ferromagnetic layer is made thinner, while the ferromagnetic layer in contact with the non-magnetic conductive layer is made thicker. With such a layered structure, it is apparently difficult to cancel a leakage magnetic field generated from the fixed magnetic layer.
A general object of the present invention is to provide a spin-valve magnetoresistive device in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a spin-valve magnetoresistive device that can prevent deviation of the magnetic direction of a free magnetic layer so that a signal magnetic field from a magnetic recording medium can be reproduced with high precision.
The above objects of the present invention are achieved by a spin-valve magnetoresistive device comprising a free magnetic layer as a first ferromagnetic layer, a non-magnetic conductive layer, a laminated fixed magnetic layer, an anti-ferromagnetic layer, and a fourth ferromagnetic layer that cancels a leakage magnetic field. In this spin-valve magnetoresistive device, the laminated fixed magnetic layer includes a second ferromagnetic layer, a reverse parallel coupling intermediate layer, and a third ferromagnetic layer, which layers are laminated in that order. Also in this spin-valve magnetoresistive device, the free magnetic layer, the non-magnetic conductive layer, the laminated fixed magnetic layer, the anti-ferromagnetic layer, and the fourth ferromagnetic layer, are laminated in that order or the reverse order.
Since the second ferromagnetic layer and the third ferromagnetic layer have opposite magnetic directions, with the reverse parallel coupling intermediate layer being interposed therebetween, a leakage magnetic field generated from the laminated fixed magnetic layer is restricted. Also, the magnetism of the fourth magnetic layer is set in such a direction that cancels the leakage magnetic field. Thus, the leakage magnetic field can be surely cancelled, and the magnetic direction of the free magnetic layer can be prevented from deviating.
With this spin-valve magnetoresistive device, a signal magnetic field from a magnetic recording medium can be reproduced with high precision.
The above objects of the present invention are also achieved by a spin-valve magnetoresistive device comprising: a first multi-layered structure that includes a free magnetic layer as a first ferromagnetic layer, a non-magnetic conductive layer, a fixed magnetic layer as a second ferromagnetic layer; and an anti-ferromagnetic layer, in that order or in the reverse order; and a second multi-layered structure that cancels a leakage magnetic field, and includes a third ferromagnetic layer, a reverse parallel coupling intermediate layer, and a fourth ferromagnetic layer, in that order. In this spin-valve magnetoresistive device, the second multi-layered structure is placed on the anti-ferromagnetic-layer side of the first multi-layered structure.
Since the second multi-layered structure cancels a leakage magnetic field from the fixed magnetic layer of the first multi-layered structure, the magnetic direction of the free magnetic layer does not deviate. Accordingly, a signal magnetic field from a magnetic recording medium can be reproduced with high precision.
The above objects of the present invention are also achieved by a spin-valve magnetoresistive device comprising: a free magnetic layer interposed between two symmetrical sets of a non-magnetic conductive layer, a fixed magnetic layer and an anti-ferromagnetic layer; and a leakage-canceling ferromagnetic layer that cancels a leakage magnetic field, and is disposed on at least one of the anti-ferromagnetic layers. In this spin-valve magnetoresistive device, the fixed magnetic layer has either a single-layered structure or a multi-layered structure that includes a ferromagnetic layer, a reverse parallel coupling intermediate layer, and another ferromagnetic layer, which layers are laminated in that order. Also, the leakage-canceling ferromagnetic layer has either a single-layered structure or a multi-layered structure that includes a ferromagnetic layer, a reverse parallel coupling intermediate layer, and another ferromagnetic layer, which layers are laminated in that order. When the fixed magnetic layer has the single-layered structure, the leakage-canceling ferromagnetic layer has the multi-layered structure. When the fixed magnetic layer has the multi-layered structure, the leakage-canceling ferromagnetic layer has the single-layered structure.
With the above dual-type SVMR device, a leakage magnetic field that has adverse influence upon the free magnetic layer can be canceled, and a signal magnetic field from a magnetic recording medium can be reproduced with high precision.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.